Microelectronic imaging devices and associated methods for attaching transmissive elements

ABSTRACT

Microelectronic imaging devices and associated methods for attaching transmissive elements are disclosed. A manufacturing method in accordance with one embodiment of the invention includes providing an imager workpiece having multiple image sensor dies configured to detect energy over a target frequency. The image sensor dies can include an image sensor and a corresponding lens device positioned proximate to the image sensor. The method can further include positioning standoffs adjacent to the lens devices while the image sensor dies are connected to each other via the imager workpiece. At least one transmissive element can be attached to the workpiece at least proximate to the standoffs so the lens devices are positioned between the corresponding image sensors and the at least one transmissive element. Accordingly, the at least one transmissive element can protect the image sensors while the image sensor dies are still connected. In a subsequent process, the image sensor dies can be separated from each other.

TECHNICAL FIELD

The present invention is directed generally toward microelectronicimaging devices and associated methods for attaching transmissiveelements, including methods for forming standoffs and attachingtransmissive elements at the wafer level.

BACKGROUND

Microelectronic imagers are used in digital cameras, wireless deviceswith picture capabilities, and many other applications. Cell phones andpersonal digital assistants (PDAs), for example, are incorporatingmicroelectronic imagers for capturing and sending pictures. The growthof microelectronic imagers has been steadily increasing as they becomesmaller and produce better images with higher pixel counts.

Microelectronic imagers include image sensors that use Charge CoupledDevice (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS)systems, or other solid-state systems. CCD image sensors have beenwidely used in digital cameras and other applications. CMOS imagesensors are also quickly becoming very popular because they are expectedto have low production costs, high yields, and small sizes. CMOS imagesensors can provide these advantages because they are manufactured usingtechnology and equipment developed for fabricating semiconductordevices. CMOS image sensors, as well as CCD image sensors, areaccordingly “packaged” to protect their delicate components and toprovide external electrical contacts.

An image sensor generally includes an array of pixels arranged in afocal plane. Each pixel is a light sensitive element that includes aphotogate, a photoconductor, or a photodiode with a doped region foraccumulating a photo-generated charge. Microlenses and color filterarrays are commonly placed over imager pixels. The microlenses focuslight onto the initial charge accumulation region of each pixel. Thephotons of light can also pass through a color filter array (CFA) afterpassing through the microlenses and before impinging upon the chargeaccumulation region. Conventional technology uses a single microlenswith a polymer coating, which is patterned into squares or circles overcorresponding pixels. The microlens is heated during manufacturing toshape and cure the microlens. Use of microlenses significantly improvesthe photosensitivity of the imaging device by collecting light from alarge light-collecting area and focusing the light onto a smallphotosensitive area of the sensor.

Manufacturing image sensors typically includes “post-processing” stepsthat occur after the microlens array is formed on a workpiece.Accordingly, it is necessary to protect the microlens array during thesepost-processing steps to prevent the microlens array from becomingcontaminated with particles that might be released during these steps.One approach to addressing the foregoing manufacturing challenge is toattach individual image sensor dies to a substrate, tape over thecorresponding sensor arrays, and then use a molding process to form“standoffs” to which a cover glass is mounted. The cover glass canaccordingly protect the image sensor during subsequent processing steps,and becomes part of the sensor package.

One drawback with this approach is that it is performed at the die leveland accordingly cannot protect the sensor arrays during processing stepsthat occur before the dies have been singulated from a correspondingwafer or other larger workpiece. Another drawback with this approach isthat a mold release agent is typically used to release the die from themold machine in which the standoffs are formed. However, the moldrelease agent tends to inhibit the adhesion of adhesive compounds, whichare required to attach the cover glass. Accordingly, the standoffsurfaces must typically be cleaned (e.g., with a plasma process) beforeattaching the cover glass. This additional cleaning step increases thecost of manufacturing the die, and reduces manufacturing throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a workpiece having multiple dies that may beprocessed and separated in accordance with an embodiment of theinvention.

FIG. 1B illustrates an imager device that includes a die singulated fromthe workpiece shown in FIG. 1A.

FIGS. 2A-2B are flow diagrams illustrating methods for processing aworkpiece in accordance with an embodiment of the invention.

FIGS. 3A-3K illustrate a process for forming imager devices at the waferlevel via a protective removable cover material and a singletransmissive element.

FIGS. 4A-4C illustrate a method for forming imager devices usingmultiple transmissive elements and a protective removable cover materialin accordance with another embodiment of the invention.

FIGS. 5A-5C illustrate a method for protecting sensitive portions of animager wafer with a mold, and applying a single transmissive element tomultiple dies in accordance with another embodiment of the invention.

FIGS. 6A-6C illustrate a method for protecting sensitive portions of animager wafer with a mold using multiple transmissive elements inaccordance with still another embodiment of the invention.

DETAILED DESCRIPTION

The following disclosure describes several embodiments of imagerworkpieces and corresponding methods for manufacturing a plurality ofmicroelectronic imaging units. A method for manufacturing a plurality ofmicroelectronic imaging units in accordance with one aspect of theinvention includes providing an imager workpiece having multiple imagesensor dies configured to detect energy over a target frequency range,the image sensor dies having an image sensor and a corresponding lensdevice positioned proximate to the image sensors. The method can, insome embodiments, further include positioning standoffs adjacent to thelens devices while the image sensor dies are connected to each other viathe imager workpiece. At least one transmissive element can be attachedto the workpiece at least proximate to the standoffs so that the lensdevices are positioned between the image sensors and the at least onetransmissive element. Individual image sensor dies can then be separatedfrom each other.

In particular aspects of the invention, positioning the standoffs caninclude disposing portions of a removable cover material on the lensdevices, positioning the imager workpiece in a mold, and forming thestandoffs by introducing a flowable mold material into the mold and intoregions between the portions of cover material. In another aspect of theinvention, positioning the standoffs can include positioning the imagerworkpiece in a mold with cover portions of the mold positioned adjacentto the lens devices. The method can further include forming thestandoffs by introducing a flowable mold material into the mold and intoregions between the cover portions of the mold, while at leastrestricting contact between the mold material and the lens devices withthe cover portions of the mold.

An imager workpiece in accordance with another aspect of the inventioncan include a substrate having multiple image sensor dies. The imagesensor dies can have image sensors configured to detect energy over atarget frequency range, and corresponding multiple lens devicespositioned proximate to the image sensors. The workpiece can furtherinclude at least one transmissive element attached to the imagerworkpiece so that the lens devices are positioned between thecorresponding image sensors and the at least one transmissive element.The at least one transmissive element can be transmissive over at leastpart of the target frequency range. In one aspect of the invention, theat least one transmissive element can include multiple transmissiveelements, with each transmissive element positioned adjacent to acorresponding image sensor die. In another aspect of the invention, theat least one transmissive element can include a single transmissiveelement positioned adjacent to multiple image sensor dies.

Specific details of several embodiments of the invention are describedbelow with reference to CMOS image sensors to provide a thoroughunderstanding of these embodiments, but other embodiments can use CCDimage sensors or other types of solid-state imaging devices. Severaldetails describing the structures and/or processes that are well knownand often associated with other types of microelectronic devices are notset forth in the following description for purposes of brevity.Moreover, although the following disclosure sets forth severalembodiments of different aspects of the invention, several otherembodiments of the invention can have different configurations ordifferent components than those described below. Accordingly, theinvention may have other embodiments with additional elements or withoutseveral of the elements described below with reference to FIGS. 1-6C.

FIG. 1A illustrates a workpiece 102 carrying multiple dies (e.g., imagerdies) 110. The workpiece 102 can be in the form of a wafer 101 or othersubstrate at which the dies 110 are positioned. Many processing stepscan be completed on the dies 110 before the dies 110 are separated orsingulated to form individual imaging devices. This approach can be moreefficient than performing the steps on singulated dies 110 because thewafer 101 is generally easier to handle than are the singulated dies110. As discussed in greater detail below, the dies 110 can includesensitive and/or delicate elements, and accordingly, it may beadvantageous to protect these elements during the wafer-level processingsteps.

FIG. 1B illustrates a finished, singulated imaging device 100 afterbeing processed in accordance with an embodiment of the invention. Theimaging device 100 can include a die 110 singulated from the workpiece102 described above with reference to FIG. 1A. The die 110 can includean image sensor 112, which can in turn include an array of pixels 113arranged in a focal plane. In the illustrated embodiment, for example,the image sensor 112 can include a plurality of active pixels 113 aarranged in a desired pattern, and at least one dark current pixel 113 blocated at a perimeter portion of the image sensor 112 to account forextraneous signals in the die 110 that might otherwise be attributed toa sensed image. In other embodiments, the arrangement of pixels 113 maybe different.

A color filter array (CFA) 114 is formed over the active pixels 113 ofthe image sensor 112. The CFA 114 has individual filters or filterelements 116 configured to allow the wavelengths of light correspondingto selected colors (e.g., red, green, or blue) to pass to each pixel113. In the illustrated embodiment, for example, the CFA 114 is based onthe RGB color model, and includes red filters, green filters, and bluefilters arranged in a desired pattern over the corresponding activepixels 113 a. The CFA 114 further includes a residual blue section 118that extends outwardly from a perimeter portion of the image sensor 112.The residual blue section 118 helps prevent back reflection from thevarious components within the die 110.

The imaging device 100 can further include a plurality of microlenses117 arranged in a microlens array 115 over the corresponding pixels 113.The microlenses 117 are used to focus light onto the initial chargeaccumulation regions of the individual pixels 113. Standoffs 140 arepositioned adjacent to the microlens array 115 to support a transmissiveelement 103. The transmissive element 103 (which can include glass) ispositioned to protect the microlens array 115 and other features of thedie 110 from contamination. Lens standoffs 104 can be mounted to thetransmissive element 103 to support a device lens 105. The device lens105 is positioned a selected distance from the microlens array 115 tofocus light onto the microlens array 115 and ultimately onto the imagesensor 112. As discussed in greater detail below, the standoffs 140 andthe transmissive element 103 can be formed on the die 110 before the die110 is singulated from the workpiece 102 (FIG. 1A) and before manyprocessing steps are completed on the die 110. Accordingly, thetransmissive element 103 can protect the underlying sensitive featuresof the die 110 during these subsequent processing steps.

FIG. 2A illustrates a process 200 for manufacturing imager devices inaccordance with an embodiment of the invention. The process 200 caninclude providing an imager workpiece that includes multiple imagesensor dies having corresponding image sensors and lens devices (processportion 201). The process can further include attaching at least onetransmissive element to the workpiece so that lens devices of theworkpiece are positioned between the image sensors and the transmissiveelement or elements (process portion 202). The process can still furtherinclude separating or singulating the image sensor dies from each other(process portion 203) after the transmissive element or elements havebeen attached to the workpiece. Accordingly, the lens devices carried bythe workpiece can be protected by the transmissive element(s) duringsingulation and, optionally, during other processes, including (but notlimited to) backgrinding the workpiece and attaching conductive elementsto the workpiece.

FIG. 2B illustrates further details of particular embodiments of theprocess described above with reference to FIG. 2A. In particular, theprocess of attaching one or more transmissive elements to the workpiece(process portion 202) can include forming standoffs (process portion205) before affixing the transmissive elements. Forming the standoffscan be accomplished in one of at least two different ways. One way caninclude shielding the lens devices of the workpiece with a removablecover material (process portion 206), placing the workpiece in a mold(process portion 207), and injecting a mold material into the mold(process portion 208). After the mold material has been applied to theworkpiece, the workpiece is removed from the mold. The workpiece canthen be background and solder balls or other conductive elements can beattached to the backside of the workpiece (process portion 211). Theseprocesses can be conducted while the removable material is in place. Inprocess portion 212, the removable cover material or shield material canbe removed, and in process 213, the transmissive element or elements canbe affixed to the workpiece.

Another method for shielding the lens devices of the workpiece includesplacing the workpiece in a mold with elements of the mold itselfpositioned to shield the lens devices (process portion 209).Accordingly, the mold elements can take the place of the removablematerial described above with reference to process portion 206. Forexample, in process portion 210, mold material is injected into the moldto form standoffs, while the mold elements shield the lens devices andprevent (or at least restrict) contact between the mold material and thelens elements. In process portion 214, one or more transmissive elementsare attached to the workpiece after the workpiece has been removed fromthe mold. Once the transmissive elements are in place, the workpiece canbe background and solder balls or other conductive elements can beattached to the back side of the workpiece (process portion 215). Afterforming the standoffs, affixing one or more transmissive elements, andpost-processing the workpiece (e.g., by backgrinding the workpieceand/or attaching conductive elements to the workpiece), individual imagesensor dies can be separated from each other (process portion 203).

FIGS. 3A-3K illustrate a method for processing imager dies while thedies remain attached to each other (e.g., at the wafer level). Theprocess illustrated in FIGS. 3A-3K uses a removable mold material and asingle transmissive element that covers multiple dies at the waferlevel. In other embodiments, the removable material can be replaced byportions of the mold itself, and/or the single transmissive element canbe replaced with multiple transmissive elements, each positioned overone of the imager dies. Further details of these other embodiments aredescribed below with reference to FIGS. 4A-6C.

Beginning with FIG. 3A, the workpiece 102 (only a portion of which isshown in FIG. 3A) can include multiple dies 110, still attached to eachother. Each die 110 can have a first surface 106, a second surface 107,and integrated circuitry 111 coupled to an image sensor 112. A colorfilter array 114 can be positioned adjacent to the image sensor 112 tofilter incoming radiation in a manner generally similar to thatdescribed above. The image sensor 112 can include multiple pixels 113,including active pixels 113 a and dark current pixels 113 b. A microlensarray 115 is positioned adjacent to the color filter array 114 andincludes multiple microlenses 117 that focus incoming radiation in amanner generally similar to that described above. Each die 110 canfurther include interconnect structures 320 for electrical communicationwith external devices. Each interconnect structure 320 can include aterminal 321 electrically coupled to the integrated circuitry 111. Theinterconnect 320 can also include a blind hole 325 and a vent hole 324.The blind hole 325 can be filled with a conductive material 326 toprovide electrical access to the integrated circuitry 111 via the secondsurface 107, after material is removed from the second surface 107. Thevent hole 324 can allow for easy entry of the conductive material 326into the blind hole 325.

The workpiece 102 can further include a scribe street 330 positionedbetween each die 110 to delineate adjacent dies 110 from each other andto provide a medium for a subsequent singulation process. The scribestreet 330 can include a scribe street slot 331 connected to athrough-wafer vent hole 333 and filled with a fill material 332. Thefill material 332 can include a non-conductive material that is disposedwithin the scribe street slot 331 prior to performing additionalprocesses on the workpiece 102. In another embodiment, the scribe streetslot 331 can be filled during a molding process, which is described ingreater detail below with reference to FIG. 3D.

As shown in FIG. 3B, a removable cover material 141 can be blanketedover the first surface 106 of the workpiece 102. The removable covermaterial 141 can include a photoresist or other selectively removablesubstance. Accordingly, portions of the cover material 141 can beselectively removed (as shown in FIG. 3C) using a masking process orother suitable process, leaving the remaining portions of cover material141 only over the microlens arrays 115. The remaining cover materialportions 141 can protect the microlens arrays 115 during subsequentprocessing steps. In a particular aspect of this embodiment, theremaining cover material portions 141 do not cover the dark currentpixels 113 b, which allows these pixels to be covered by mold material,as described below.

Referring next to FIG. 3D, the workpiece 102 can be positioned in a mold350, between a lower mold portion 352 and an upper mold portion 351. Thelower mold portion 352 can include a removable layer of lower mold tape354, and the upper mold portion 351 can include a removable layer ofupper mold tape 353. The lower mold tape 354 and upper mold tape 353 canprevent direct contact between the mold material and the mold surfacesto allow the workpiece 102 to be easily removed after the moldingprocess.

During the molding process, a mold material 355 is injected into themold 350 to fill the regions between the portions of cover material 141.Accordingly, the mold material 355 can form the standoffs 140 betweenthe microlens arrays 115 of neighboring dies 110. The standoffs 140 canbe positioned to cover the dark current pixels 113 b so that thesepixels do not receive radiation during normal use. If the scribe streetslot 331 between neighboring dies 110 was not previously filled with afill material, the mold material 355 can fill the scribe street slot 331during the molding process. After the molding process, the upper moldportion 351 and the lower mold portion 352 are moved away from eachother allowing the workpiece 102 to be removed.

FIG. 3E illustrates the workpiece 102 after it is removed from the mold350 and inverted for backgrinding. During the backgrinding process, agrinder 360 removes a selected thickness of material from the secondsurface 107. In one aspect of this embodiment, the selected thicknesscan be one that exposes an end 334 of the scribe street 330, withoutexposing the ends 327 of the interconnect structures 320.

As shown in FIG. 3F, an etching process or other selective removalprocess can be used to remove further material from the second surface107 so that the interconnect ends 327 project from the second surface107, with the scribe street end 334 projecting from the second surface107 by a greater distance. A protective coating 361 (FIG. 3G) can beapplied to the second surface 107 to cover the interconnect ends 327 andthe scribe street end 334. As shown in FIG. 3H, the protective coating361 and the scribe street 330 can be ground or etched so that theinterconnect ends 327 are again exposed. The manufacturer can thenattach connectors 322 (e.g., solder balls) to the interconnect ends 327to provide for electrical communication with the integrated circuitry111 located within each of the dies 110. During the foregoing processes(e.g., the backgrinding process and the connector attachment process),the protective cover material 141 remains in place over the microlensarrays 115 to prevent particulates and/or other contaminants fromcontacting the microlens arrays 115.

FIG. 3I illustrates the workpiece 102 after the cover material 141 hasbeen removed via a suitable process (e.g., an etching process). Afterthe cover material 141 has been removed, the standoffs 140 remain inposition adjacent to each of the microlens arrays 115. Because the moldmaterial forming the standoffs 140 abutted the tape layers 353, 354described above with reference to FIG. 3D, the exposed surfaces of thestandoffs 140 have not been coated with a mold release agent.Accordingly, the standoffs 140 are ready to be attached to atransmissive member (e.g., a cover glass) without first requiring that arelease agent be removed from the standoffs 140.

FIG. 3J illustrates the transmissive element 103 attached to thestandoffs 140 with attachment elements 308. The attachment elements 308can include adhesive layers in one embodiment. In another embodiment,the surface of each of the standoffs 140 adjacent to the transmissiveelement 103 can be softened or otherwise activated so that the moldmaterial 355 itself attaches directly to the transmissive element 103.In any of these embodiments, after the transmissive element 103 has beenattached to the workpiece 102, a dicing wheel 362 or other separatingtool can be aligned with the scribe street 330 and activated to separateneighboring dies 110 from each other.

FIG. 3K illustrates a singulated die 110 having standoffs 140 that carrya singulated portion of the transmissive element 103 to protect theunderlying sensitive structures. At this point, the sides 309 of the die110 can be treated to remove residual material (e.g., residual scribestreet material), and the resulting device 100 can be completed byattaching lens standoffs 104 and a device lens 105 and (both shown inFIG. 1B) adjacent to the transmissive element 103.

One feature of an embodiment of the process described above withreference to FIGS. 3A-3K is that several steps of the process can becompleted on multiple dies 110 while the dies 110 remain attached to thecorresponding workpiece 102, e.g., at the wafer level. These processescan include, but are not limited to a backgrinding process and aconnector attachment process. During these processes, the microlensarrays 115 and underlying sensitive imager structures can be protectedby the removable cover material 141. Accordingly, these processes can becompleted without damaging the microlens arrays 115 and underlyingstructures. In addition, the standoffs 140 formed by the mold processcan be positioned to cover the dark current pixels 113 b. Accordingly, aseparate step need not be employed to cover these pixels. An advantageof the foregoing processes is that it may be more efficient andtherefore cost effective to carry out the processes at the wafer levelrather than at the die level. Another advantage is that the wafer iseasier to handle and less subject to breakage than are individual dies110. Accordingly, by carrying out these processes at the wafer level,the number of steps requiring handling individual dies 110 can bereduced, which can in turn reduce the number of dies 110 that aredamaged or destroyed during these process steps.

Another advantage of using the mold process described above is that theheight of each of the standoffs 140 can be precisely controlled bycontrolling the manufacture of the mold 350 and the relative spacing ofthe upper and lower mold portions 351, 352 during the molding process.As a result, the location of the device lens 105 relative to themicrolens array 115 can also be precisely controlled and can ensure thatradiation is precisely focused on the microlens array 115. This processcan also be used to ensure that the distance between the microlens array115 and the transmissive element 103 exceeds a threshold value.Accordingly, contaminants (should they exist) on the surface of thetransmissive element 103 may tend to create shadows that are out offocus and/or blurry. The effect of such contaminants on the pixels 113can therefore be reduced.

Another feature of embodiments of the foregoing processes is that theycan include forming molded standoffs without the use of a mold releaseagent. Instead, a layer of releasable tape (having an inwardly facing,non-stick surface) can be applied to the mold to prevent adhesionbetween the mold and the mold material. An advantage of this arrangementis that it can eliminate the step of cleaning the standoffs prior toadhering the transmissive element(s) to the standoffs. Accordingly, thisapproach can reduce processing time and increase throughput, whether itis performed at the water level or on individual dies.

FIGS. 4A-4C illustrate a process that is generally similar to theprocess described above with reference to FIGS. 3A-3K, but includesdisposing multiple transmissive elements (e.g., one for each die) ratherthan a single transmissive element that covers multiple dies. Forpurposes of brevity, many of the steps described above with reference toFIGS. 3A-3K are not repeated in the discussion below. Beginning withFIG. 4A, the workpiece 102 can be positioned in a mold 450 having alower mold portion 452 carrying a lower mold tape 454, and an upper moldportion 451 carrying an upper mold tape 453. The upper mold portion 451can include mold cutouts 456 and a vacuum process can be used to conformthe upper mold tape 453 to the contours of the upper mold 451. When themold material 355 is injected into the mold 450 between adjacentportions of the cover material 141, it extends into and fills the moldcutouts 456 and forms correspondingly shaped standoffs 440.

FIG. 4B illustrates the workpiece 102 after (a) it has been removed fromthe mold 450, (b) the second surface 107 has been ground, (c) theconnectors 322 have been attached, and (d) the cover material portions141 have been removed. Each of the standoffs 440 includes a recess 442sized to receive a corresponding transmissive element that is positionedadjacent to only a single one of the dies 110.

FIG. 4C illustrates one of the dies 110 after a transmissive element 403has been attached to the standoffs 440, and after the die 110 has beensingulated from the workpiece 102 (FIG. 4B). The transmissive element403 can be attached to the corresponding standoffs 440 using any of theadhesion processes described above.

FIGS. 5A-5C illustrate a method for processing the workpiece 102 andprotecting the microlens arrays 115 without the use of a removable covermaterial 141. Instead, the mold itself can provide protection for themicrolens arrays 115. Beginning with FIG. 5A, a mold 550 can include anupper mold portion 551 having cavities 557 and intermediate projections558 or cover portions carrying a conformal upper mold tape layer 553.The upper mold portion 551 can be positioned adjacent to a lower moldportion 552 that carries a layer of lower mold tape 554. When theworkpiece 102 is positioned between the upper mold portion 551 and thelower mold portion 552, the two mold portions can be brought intoproximity with each other until the projections 558 (and the upper moldtape layer 553 carried by the projections 558) contact the underlyingmicrolens arrays 115. The mold material 355 is then injected into themold 550 to fill the cavities 557 and form corresponding standoffs 540.

FIG. 5B illustrates the workpiece 102, with standoffs 540, after theworkpiece 102 has been removed from the mold 550. FIG. 5C illustratesthe workpiece 102 after the transmissive element 103 has been attachedto the standoffs 540, prior to backgrinding, attaching connectors, andsingulating the neighboring dies 110. These processes can be completedin a manner generally similar to that described above with reference toFIGS. 3E-3J.

FIGS. 6A-6C illustrate a process that is generally similar to thatdescribed above with reference to FIGS. 5A-5C, but is configured toapply individual transmissive elements 103 to each of the dies 110.Beginning with FIG. 6A, the workpiece 102 can be positioned in asuitable mold 650 that includes an upper mold portion 651 having moldcutouts 656. The upper mold portion 651 is positioned adjacent to alower mold portion 652, with the substrate 102 positioned there between.The mold compound 355 is injected into the mold 650 so as to formstandoffs 640, each of which has a recess 642 (FIG. 6B). Accordingly, asshown in FIG. 6C, the standoffs 640 can support individual transmissiveelements 603 for each of the imager dies 110.

One feature of embodiments of the foregoing processes described abovewith reference to FIGS. 5A-6C is that they can include a mold that isshaped to protect sensitive portions of the workpiece during the moldingprocess. Accordingly, these processes need not include coating portionsof the workpiece with a removable cover material. An advantage of thisarrangement is that it can reduce the number of process steps associatedwith forming the standoffs.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from theinvention. For example, aspects of the invention described in thecontext of particular embodiments may be combined or eliminated in otherembodiments. Further, while advantages associated with certainembodiments of the invention have been described in the context of thoseembodiments, other embodiments may also exhibit such advantages, and notall embodiments need necessarily exhibit such advantages to fall withinthe scope of the invention. Various features associated with some of theprocesses described above (e.g., the formation of the interconnectstructures) are described in greater detail in other pendingapplications assigned to the assignee of the present application. Theseapplications include U.S. application Ser. No. 11/056,211, filed on Feb.10, 2005 and U.S. application Ser. No. 11/217,877, filed on Sep. 1,2005, both of which are incorporated herein in their entireties byreference. Accordingly, the invention is not limited except as by theappended claims.

1. A method for manufacturing a plurality of microelectronic imagingunits, comprising: providing an imager workpiece having multiple imagesensor dies, the image sensor dies having image sensors configured todetect energy over a target frequency range and corresponding lensdevices positioned proximate to the image sensors, the image sensorsincluding dark pixels; attaching at least one transmissive element tothe workpiece via standoffs so that the lens devices are positionedbetween the corresponding image sensors and the at least onetransmissive element while the image sensor dies are connected to eachother via the imager workpiece, the at least one transmissive elementbeing transmissive over at least part of the target frequency range andthe standoffs being positioned to cover the dark pixels in the imagesensors; and separating the image sensor dies from each other afterattaching the at least one transmissive element.
 2. The method of claim1 wherein attaching at least one transmissive element includes:disposing portions of a removable cover material adjacent to the lensdevices, the dark pixels not being covered by the portions of covermaterial; positioning the imager workpiece in a mold; and forming thestandoffs by introducing a flowable mold material into the mold and intoregions between the portions of cover material.
 3. The method of claim 1wherein attaching at least one transmissive element includes:positioning the imager workpiece in a mold, with cover portions of themold positioned adjacent to the lens devices, the dark pixels not beingcovered by the cover portions of the mold; and forming the standoffs byintroducing a flowable mold material into the mold and into regionsbetween the cover portions of the mold, while at least restrictingcontact between the mold material and the lens devices with the coverportions of the mold.
 4. The method of claim 1 wherein attaching atleast one transmissive element includes attaching multiple transmissiveelements with each transmissive element positioned adjacent to acorresponding image sensor die.
 5. The method of claim 1 whereinattaching at least one transmissive element includes attaching a singletransmissive element positioned to transmit energy to multiple imagesensor dies.
 6. The method of claim 1 wherein the imager workpieceincludes a first surface and a second surface facing opposite from thefirst surface, with the image sensors positioned proximate to the firstsurface, and wherein the method further comprises: placing a removablecover material adjacent to the lens devices; removing material from thesecond surface of the imager workpiece while the cover material ispositioned adjacent to the lens devices; removing the cover material;and attaching the at least one transmissive element to the workpieceafter removing the cover material.